Aerial assembly



April 28, 1959 i A. G. G. H. ROBINSON 2,384,630

AERIAL ASSEMBLY Filed March 22, 1957 I 2 Sheets-Shet 1 Inventor April 2 8, 1959 A. G. G; H. ROBINSON 2,884,630

AERIAL ASSEMBLY Filed March 22, 1957 2 Sheets-Shet 2 Inventor Q tkM QoHnson A Item e y;

United States Patent AERIAL ASSEMBLY Arthur G. G. H. Robinson, Malmesbury, England, asflglllol to E. K. Cole Limited, Southend-on-Sea, Eng- Application March 22, 1957, Serial No. 647,899

Claims priority, application Great Britain March 27, 1956 9 Claims. (Cl. 343-756) Many micro-wave aerial assemblies consist of a wave guide or co-axial feed which directs the microwave radiation at a reflector, and a dipole aerial may be used in conjunction with the wave guide or co-axial feed. The term aerial will be used hereafter as a general description of the source from which transmitted radiation is directed at a reflector in an aerial assembly.

It is sometimes desired readily to change from one required pattern of radiation to another and an object of the present invention is to provide that facility.

A particular application of the invention is to an aerial assembly for an airborne search radar system, where it is required to have a pattern of radiation in the form of a pencil beam for the location of airborne objects and an alternative pattern of radiation in the form of a beam obeying the cosecant-squared law for eflicient map reading of the ground below.

A feature of my invention is a micro-wave aerial assembly for providing at least two alternative required patterns of radiation, comprising an aerial, a main reflector for determiningone of said required patterns of radiation, an auxiliary reflector, and means for effecting movement of the auxiliary reflector, through the main reflector, between two alternative positions, in a first of which the main reflector is located between the auxiliary reflector and the areial and in which the auxiliary reflector has negligible eflect on the required pattern of radiation determined by the main reflector and in the second of which positions the auxiliary reflector is located between the main reflector and the aerial and determines an alternative required pattern of radiation.

The above and other features of the invention will be more readily understood by a perusal of the following description having reference to the accompanying drawings in which Figure 1 is a diagrammatic front elevation of an aerial assembly constructed on known principles, and, Figure 2 is a sectional side elevation of the reflector portions thereof. Figure 3 is a similar view to Figure 2, but showing one embodiment of my invention. Figures 4 and 5 show a sectional side elevation and a rear elevation respectively of another embodiment of my invention.

In Figures 1 and 2 an aerial A (not shown in detail), with the electric vector E orientated in the direction shown by the arrow, is mounted at or near the focal point of a main reflector B designed according to known principles to produce one required pattern of radiation. An auxiliary reflector C in the form of a series of thin parallel plates is mounted within the main reflector B. These plates are successively spaced apart by less than one-half wavelength and have leading edges which determine an alternative required pattern of radiation when the plates are positioned with respect to the feed from A so that the voltage vector of the incident radiation is parallel to them (as in Figure 1). Under these conditions, the plates behave as wave guides beyond cut-off and radiation is reflected from them in the vicinity of their leading edges. When the plates of reflector C occupy a position at right angles to that which they occupy in Figure 1 (the aerial ice remaining in the same position), they have negligible etfect on the pattern of radiation determined by the main reflector, the radiation passing between them and being reflected by the main reflector B.

This change of relative position between the aerial A and the auxiliary reflector C and can be effected by causing A or C to be rotatable.

One embodiment of the invention is shown in Figure 3. In this case the main reflector B has vertical narrow slots through which may pass the plates of the auxiliary reflector C, the aerial (not shown) being mounted at or near the focal point of the main reflector B. When the auxiliary reflector C is in effective operation, a front elevation would be the same as Figure 1, the plates of reflector C protruding between the main reflector and the aerial, so that the auxiliary reflector determines the alternative required pattern of radiation, whereas by swinging the plates about a pivot D, the reflector C may be moved to a position to the rear of the main reflector, as in Figure 3, where C has negligible effect on the pattern of radiation determined by the main reflector B. The slots are very narrow compared with wavelength and are parallel to the voltage vector of the incident radiation. The slots thus have negligible effect on the pattern of radiation determined by the main reflector.

The auxiliary reflector C may be in the form of a grating and its movement may be eflfected alternatively by sliding the plates through the slots in the main reflector instead of pivoting them as in the assembly of Figure 3. Such an arrangement is shown in Figures 4 and 5, in which the auxiliary reflector C slides on guides F through the main reflector B.

The pattern of radiation from the aerial determined by the main reflector may be in the form of a pencil beam and the alternative pattern of radiation determined by the auxiliary reflector may be in the form of a beam obeying the so-called cosecant-squared law.

This invention is also applicable to aerial assemblies in which the auxiliary reflector is so large that it is impracticable to rotate it according to known methods of beam switching, and where it is not permissible to rotate the feed because of unwanted effects from the resultant change of polarisation.

I claim:

1. A micro-wave aerial assembly for providing at least two alternative required patterns of radiation, comprising an aerial, a main reflector for determining one of said required patterns of radiation, an auxiliary reflector, and means for effecting movement of the auxiliary reflector, through the main reflector, between two alternative positions, in a first of which the main reflector is located between the auxiliary reflector and the aerial and in which the auxiliary reflector has negligible effect on the required pattern of radiation determined by the main reflector and in the second of which positions the auxiliary reflector is located between the main reflector and the aerial and determines an alternative required pattern of radiation.

2. An aerial assembly according to claim 1, comprising pivoting means near an edge of the main reflector, the auxiliary reflector being pivotable about said pivoting means between said first and second positions.

3. An aerial assembly according to claim 1, comprising means for slidably moving the auxiliary reflector through the main reflector between said first and second positions.

4. An aerial assembly according to claim 2, in which the auxiliary reflector comprises a plurality of thin plates having leading edges which determine the reflecting surface, said plates being substantially parallel and being successively spaced apart by a distance less than one-half wavelength, the main reflector having narrow slots through which the plates are movable, and in which radiation transmitted by the aerial has a voltage vector which is parallel with said plates.

5. An aerial assembly according to claim 3, in which the auxiliary reflector comprises a plurality of thin plates having leading edges which determine the reflecting surface, said plates being substantially parallel and being successively spaced apart by a distance less than onehalf wavelength, the main reflector having narrow slots through which the plates are movable, and in which radiation transmitted by the aerial has a voltage vector which is parallel with said plates.

6. An aerial assembly according to claim 4, in which the main reflector is of the paraboloid type, the aerial being situated at least in the near vicinity of the focal point of the main reflector.

7. An aerial assembly according to claim 5, in which the main reflector is of the paraboloid type, the aerial be- 4 ing situated at least in the near vicinity of the focal point of the main reflector.

8. An aerial assembly according to claim 2, in which in said first position, the required pattern of radiation comprises a pencil beam and in which, in said second position, the alternative required pattern of radiation comprises a beam obeying the so-called cosecant-squared law.

9. An aerial assembly according to claim 3, in which in said first position, the required pattern of radiation comprises a pencil beam and in which, in said second position, the alternative required pattern of radiation comprises a beam obeying the so-called cosecant-squared law.

Bohnert et al. Oct. 9, 1951 Sichak Apr. 23, 195 

